sex 
(sĕks)
(sĕks)n.
1.
a. Sexual activity, especially sexual intercourse: hasn't had sex in months.
b. The sexual urge or instinct as it manifests itself in behavior: motivated by sex.
2.
a. Either of the two divisions, designated female and male, by which most organisms are classified on the basis of their reproductive organs and functions: How do you determine the sex of a lobster?
b. The fact or condition of existing in these two divisions, especially the collection of characteristics that distinguish female and male: the evolution of sex in plants; a study that takes sex into account. See Usage Note at gender.
3. Females or males considered as a group: dormitories that house only one sex.
4. One's identity as either female or male.
5. The genitals.
tr.v. sexed, sex·ing, sex·es
1. To determine the sex of (an organism).
2. Slang
a. To arouse sexually. Often used with up.
b. To increase the appeal or attractiveness of. Often used with up.
[Middle English, from Latin sexus.]